Game is meant to be balanced in 1vs1 and 2vs2.
Plenty of big open maps in those game modes too. Lots of empty space in some of them that take infantry a long time to traverse.
Kubels will be especially good on Arnhem, Semois and crossing in the wood insofar as 1v1 is concerned. Arnhem has lots of wide flanks, hiding spots and cut offs (On roads no less). Semois has a lot of distant points that are a bitch to hold. Crossing in the wood likewise has a cut off on a god damn road which makes it easy for a kubel to zip over.
Mines will help, but I think you're underestimating how survivable a kubel will be and how far behind it will put people. It'll hide on the edges of the map and harass while he's otherwise engaged or unable to defend. The more units he commits to going after the kubel, the less he has fighting your other units. That's the strength of a highly mobile capping unit: you can fight with your other units instead of worrying about capping.